Smart cards are widely used, for many different purposes. The data may be transmitted between the smart card and the reader by the use of contacts, or without contacts. In the case of non-contacting data transmission, the data is transmitted by means of an electromagnetic field.
The smart card has transmitting and receiving devices for bidirectional communication. If only unidirectional communication is intended, the circuitry complexity is reduced as a function of the intended communication direction.
The quality of the data transmission and, associated with it, the transmission reliability between the non-contacting smart card and the reader as well fluctuate, for example because of electromagnetic field strength changes at the location of the receiver. These are caused by distance changes between the smart card and the reader during communication, as can occur when the smart card is used as access authorization to be read on passing by, for example as a ski pass.
A further factor which adversely affects communication is temperature. Severely fluctuating ambient temperatures, which affect smart cards which, for example, are used as access authorization both within and outside buildings, can influence the communication.
Until now, integrated circuits on the smart cards have been designed so as to ensure adequate communication quality for an operating area that is as large as possible, or for the entire relevant operating area. Areas such as these are specified, for example, by the ISO Standard.
One major element for receiving transmitted data is a demodulator, which converts an analog input signal to a demodulated signal, which can be further-processed.
Until now, an analog demodulator such as this was tested before being brought into use, and the drive parameters were optimized for a wide operating area, or for a preferred operating area, and were then stored within the circuitry. The first case represents a compromise solution. In the latter case, discrepancies from the preferred operating area lead to reduced communication quality.
This matching process is carried out only once. The demodulator setting is therefore fixed, and can no longer be changed during operation.